Around 100 million years ago, our planet experienced a series of catastrophic events that forever altered its evolutionary path. Scientists have long puzzled over the environmental crises that wiped out vast marine species, but recent research offers fresh insights into what caused these drastic changes. According to a new study by experts from the University of Southampton, these devastating events were triggered by significant geological forces, reshaping the planet’s ecosystems and leading to widespread extinctions. The findings, now published in Nature Geoscience, offer a deeper understanding of the dramatic shifts that occurred during the Mesozoic era.

Oceanic Anoxic Events and Their Triggers

Between 185 and 85 million years ago, the Earth experienced a series of severe environmental crises known as oceanic anoxic events. These events, characterised by the depletion of dissolved oxygen in the seas, have long baffled scientists. However, a new study sheds light on the triggers behind these crises, revealing how they led to mass extinctions in marine ecosystems. The research, led by Professor Tom Gernon from the University of Southampton, highlights the impact of plate tectonics on ocean chemistry during the Jurassic and Cretaceous periods, collectively known as the Mesozoic era.

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Impact of Gondwana's Breakup on Ocean Chemistry

The study explores how the breakup of the supercontinent Gondwana influenced the chemical cycles within the oceans. Gondwana, which comprised about two-thirds of today’s continental area, was a vast landmass where dinosaurs once roamed. Professor Gernon explained that the disintegration of Gondwana spurred intense volcanic activity worldwide. As tectonic plates shifted and new seafloors formed, large quantities of phosphorus, a vital nutrient for life, were released into the oceans from weathering volcanic rocks. This influx of phosphorus significantly disrupted the oceanic chemical balance, triggering drastic biological changes.

The Aftermath: Dead Zones and Mass Extinctions

Professor Gernon described these events as a "geological tag team," where multiple pulses of chemical weathering on both the seafloor and continents alternately destabilised marine environments. The study’s findings suggest that these pulses coincided with the most significant oceanic anoxic events recorded in geological history.

The influx of phosphorus initially fueled marine life growth, but it came at a heavy cost. As vast amounts of organic matter sank to the ocean floor, it consumed large quantities of oxygen, creating extensive “dead zones” where oxygen levels were too low to support most marine life. Co-author Professor Benjamin Mills from the University of Leeds noted that these anoxic conditions led to the widespread extinction of marine species.

These catastrophic events, which lasted between one to two million years, had a profound impact on marine ecosystems—a legacy that continues to influence the oceans today. The study not only provides a clearer understanding of the forces that reshaped Earth's past but also offers insights into the complex interplay between geology and biology that continues to shape our planet.

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